1. Field of Invention
This invention relates to a semiconductor device made up of a semiconductor substrate, a flexible area isolated from the semiconductor substrate and displaced in response to temperature change, and a heat insulation area placed between the semiconductor substrate and the flexible area, a semiconductor microactuator using the semiconductor device, a semiconductor microvalve, a semiconductor microrelay, and a semiconductor microactuator manufacturing method.
2. Related Art
A semiconductor microactuator includes at least two materials having different thermal expansion coefficients in combination as a bimetal structure wherein the bimetal structure is heated and the difference between the thermal expansion coefficients is used to provide displacement is available as a mechanism using a semiconductor device made up of a semiconductor substrate, a flexible area isolated from the semiconductor substrate and displaced in response to temperature change, and a heat insulation area placed between the semiconductor substrate and the flexible area. The semiconductor microactuator is disclosed in U.S. Pat. No. 5,069,419 xe2x80x9cSemiconductor microactuator.xe2x80x9d
A semiconductor microactuator described in U.S. Pat. No. 5,069,419 is as shown in FIG. 53 (top view) and FIG. 54 (sectional view); it has a flexible area of a bimetal structure comprising an aluminum thin film 304 formed in a part of a silicon diaphragm 300. If an electric current is made to flow into a heater 301 formed in the silicon diaphragm 300, heat is generated and the temperature of the diaphragm 300 rises. Since silicon and aluminum differ largely in thermal expansion coefficient, a thermal stress occurs, bending the diaphragm 300, producing displacement of a moving part 305 placed contiguous with the diaphragm 300. To provide efficient displacement, a hinge 303 of a silicon dioxide thin film is placed between the periphery of the diaphragm 300 and a silicon frame 302 of a semiconductor substrate for preventing heat generated in the diaphragm 300 from escaping to the silicon frame 302.
However, considering the current state of application, it is desired to furthermore decrease the heat loss. Specifically, the heat escape (heat loss) is thought of as power (consumption power) supplied all the time to maintain the diaphragm 300 at a predetermined temperature (for example, 150xc2x0 C.).
Then, it is desired that the power consumption is 100 mW or less considering miniature, portable battery-driven applications.
Further, as examples of semiconductor microrelays in related arts, semiconductor microrelays are disclosed in JP-A-6-338244 and JP-A-7-14483. The semiconductor microrelays disclosed therein will be discussed with reference to the accompanying drawing.
FIG. 55 is a sectional view to show the structure of the semiconductor microrelay in the related art. As shown in FIG. 55, the semiconductor microrelay has a cantilever beam 313 having a first thermal expansion coefficient and made of a silicon monocrystalline substrate 312 with an opposite end supported so that one end can be moved. On the rear side of the cantilever beam 313, the semiconductor microrelay has a metal layer 315 having a second thermal expansion coefficient larger than the first thermal expansion coefficient via a conductive layer 315. On the main surface of the cantilever beam 313, a contact circuit 317 is provided via an oxide film 314 on the one end side. Also, a heater circuit 318 is provided via the oxide film 314 on the roughly full face of the main surface of the cantilever beam 313.
On the other hand, an opposed contact part 320 having a conductive layer 319 as an opposed surface is provided at a position facing the contract circuit 317 with a predetermined space above the contract circuit 317. An electric current is made to flow into the heater circuit 318, whereby the heater circuit 318 is heated. Thus, a flexible area consisting of the cantilever beam 313 and the metal layer 316 is heated. At this time, the thermal expansion coefficient of the metal layer 316 is set larger than that of the cantilever beam 313, so that the cantilever beam 313 and the metal layer 316 are displaced upward. Therefore, the contact circuit 317 provided on the one end of the cantilever beam 313 is pressed against the opposed contact part 320 and is brought into conduction. Such a bimetal-driven relay enables an increase in the contact spacing and an increase in the contact load as compared with a conventional electrostatically driven relay. Thus, a relay with small contact resistance and good reliability with less welds, etc., can be provided.
However, the semiconductor microrelay in the related art also involves the following problem: To drive the relay, it is necessary to make an electric current flow into the heater circuit 318 provided on the main surface of the cantilever beam 313 for heating the cantilever beam 313 and the metal layer 316. However, the silicon monocrystal forming the cantilever beam 313 is a material having very good thermal conductivity, the cantilever beam 313 is connected at the opposite end to the silicon monocrystalline substrate 312, and large heat is escaped from the cantilever beam 313 to the silicon monocrystalline substrate 312, so that it becomes extremely difficult to raise the temperature of the cantilever beam 313 with small power consumption.
That is, with the semiconductor microrelay in the related art, large power must be supplied all the time to maintain the conduction state. The value is extremely large as compared with a mechanical relay that can be driven with several ten mW. For practical use, realizing low power consumption is a large challenge.
As described above, the semiconductor microactuator using the semiconductor device, the semiconductor microvalve, and the semiconductor microrelay in the related arts require large power consumption and thus it becomes difficult to drive them with a battery and it is made impossible to miniaturize them for portable use.
It is therefore an object of the invention to provide a semiconductor device with small power consumption, manufactured by an easy manufacturing process, a semiconductor microactuator using the semiconductor device, a semiconductor microvalve, a semiconductor microrelay, and a semiconductor microactuator manufacturing method.
To the end, according to a first aspect of the present invention, there is provided a semiconductor device comprising a semiconductor substrate, a flexible area being isolated from the semiconductor substrate and displaced in response to temperature change, and a thermal insulation area being placed between the semiconductor substrate and the flexible area and made of a resin for joining the semiconductor substrate and the flexible area. The thermal insulation area made of a resin is placed between the semiconductor substrate and the flexible area, whereby heat escape when the temperature of the flexible area is changed is prevented, so that power consumption can be suppressed and further the manufacturing method is simple.
In a second aspect to the present invention, in the semiconductor device as first aspect of the present invention, the material of which the thermal insulation area is made has a thermal conductivity coefficient of about 0.4 W/(m xc2x0 C.) or less. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced.
In a third aspect of the present invention, in the semiconductor device as the second aspect of the present invention, the material of which the thermal insulation area is made is polyimide. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced and manufacturing the semiconductor device is facilitated.
In a fourth aspect of the present invention, in the third aspect of the present invention, the material of which the thermal insulation area is made is a fluoridated resin. The heat insulation properties between the flexible area and the semiconductor substrate are enhanced and manufacturing the semiconductor device is facilitated.
In a fifth aspect of the present invention, in the first to fourth aspect of the present invention, a reinforcement layer made of a harder material than the material of which the thermal insulation area is made is provided on at least one face orthogonal to a thickness direction of the thermal insulation area. The joint strength of the semiconductor substrate and the flexible area can be increased.
In a sixth aspect of the present invention, in the fifth aspect of the present invention, the reinforcement layer has a Young""s modulus of 9.8xc3x97109 N/m2 or more. The joint strength of the semiconductor substrate and the flexible area can be increased.
In a seventh aspect of the present invention, in the sixth aspect of the present invention, the reinforcement layer is a silicon dioxide thin film. The joint strength of the semiconductor substrate and the flexible area can be increased.
In an eighth aspect of the present invention, in the first to seventh aspect of the present invention, the portions of the semiconductor substrate and the flexible area in contact with the thermal insulation area form comb teeth. The joint strength of the semiconductor substrate and the flexible area can be increased.
According to a ninth aspect of the present invention, there is provided a semiconductor device comprising a semiconductor device as the first to eighth aspect of the present invention and a moving element placed contiguous with the flexible area, wherein when temperature of the flexible area changes, the moving element is displaced relative to the semiconductor substrate. The semiconductor device which has similar advantages to those in the invention as claimed in claims 1 to 8 as well as can be driven with low power consumption can be provided.
In a tenth aspect of the present invention, in the ninth aspect of the present invention, the flexible area has a cantilever structure. The semiconductor device can be provided with large displacement of the moving element.
In an eleventh aspect of the present invention, in ninth aspect of the present invention, the moving element is supported by a plurality of flexible areas. The moving element can be supported stably.
In a twelfth aspect of the present invention, in the eleventh aspect of the present invention, the flexible areas are in the shape of a cross with the moving element at the center. Good displacement accuracy of the moving element can be provided.
In a thirteenth aspect of the present invention, in the ninth aspect of the present invention, displacement of the moving element contains displacement rotating in a horizontal direction to a substrate face of the semiconductor substrate. The displacement of the moving element becomes large.
In a fourteenth aspect of the present invention, in the eleventh or thirteenth aspect of the present invention, the flexible areas are four flexible areas each shaped like L, the four flexible areas being placed at equal intervals in every direction with the moving element at the center. The lengths of the flexible areas can be increased, so that the displacement of the moving element can be made large.
In a fifteenth aspect of the present invention, in the ninth to fourteenth aspect of the present invention, the flexible area is made up of at least two areas having different thermal expansion coefficients and is displaced in response to the difference between the thermal expansion coefficients. As the temperature of the flexible area is changed, the flexible area can be displaced.
In a sixteenth aspect of the present invention, in the fifteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of aluminum. As the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between aluminum and silicon.
In a seventeenth aspect of the present invention, in the fifteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of nickel. As the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between nickel and silicon.
In a eighteenth aspect of the present invention, in the fifteenth aspect of the present invention, at least one of the areas making up the flexible area is made of the same material as the thermal insulation area. Since the flexible area and the thermal insulation area can be formed at the same time, the manufacturing process is simplified and the costs can be reduced.
In a nineteenth aspect of the present invention, in the eighteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of polyimide as the area made of the same material as the thermal insulation area. In addition to a similar advantage to that in the invention, as the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between silicon and polyimide, and the heat insulation properties of the flexible area owing to polyimide.
In a twentieth aspect of the present invention the invention, in the eighteenth aspect of the present invention, the flexible area includes an area made of silicon and an area made of a fluoridated resin as the area made of the same material as the thermal insulation area. In addition to a similar advantage, as the temperature of the flexible area is changed, the flexible area can be displaced because of the thermal expansion difference between silicon and the fluoridated resin, and the heat insulation properties of the flexible area owing to the fluoridated resin.
In a twenty-first aspect of the present invention, in the ninth to fourteenth aspect of the present invention, the flexible area is made of a shape memory alloy. As the temperature of the flexible area is changed, the flexible area can be displaced.
In a twenty-second aspect of the present invention, in the ninth to twenty-first aspect of the present invention, a thermal insulation area made of a resin for joining the flexible area and the moving element is provided between the flexible area and the moving element. The heat insulation properties between the flexible area and the moving element can be provided and power consumption when the temperature of the flexible area is changed can be more suppressed.
In a twenty-third aspect of the present invention, in the twenty-second aspect of the present invention, wherein rigidity of the thermal insulation area provided between the semiconductor substrate and the flexible area is made different from that of the thermal insulation area provided between the flexible area and the moving element. The displacement direction of the moving element can be determined depending on the rigidity difference between the thermal insulation areas.
In a twenty-fourth aspect of the present invention, in the ninth to twenty-third aspects of the present invention, the flexible area contains heat means for heating the flexible area. The semiconductor device can be miniaturized.
In a twenty-fifth aspect of the present invention, in the ninth to twenty-fifth aspects of the present invention, wiring for supplying power to the heat means for heating the flexible area is formed without the intervention of the thermal insulation area. The heat insulation distance of the wiring can be increased and the heat insulation properties of the flexible area can be enhanced.
In a twenty-sixth aspect of the present invention, in the ninth to twenty-fifth aspect of the present invention, the moving element is formed with a concave part. The heat capacity of the moving element is lessened, so that the temperature change of the flexible area can be accelerated.
In a twenty-seventh aspect of the present invention, in the ninth to twenty-sixth aspects of the present invention, a round for easing a stress is provided in the proximity of the joint part of the flexible area and the moving element or the semiconductor substrate. The stress applied in the proximity of the joint part when the flexible area is displaced is spread by means of the round, whereby the part can be prevented from being destroyed.
In a twenty-eighth aspect of the present invention, in the twenty-seventh aspect of the present invention, the semiconductor substrate is formed with a projection part projecting toward the joint part to the flexible area and the round is formed so that the shape of the round on the substrate face on the semiconductor substrate becomes like R at both ends of the base end part of the projection part. The stress applied to both ends of the base end part of the projection part when the flexible area is displaced is spread by means of the round, whereby the portion can be prevented from being destroyed.
In a twenty-ninth aspect of the present invention, in twenty-seventh aspect of the present invention, the semiconductor substrate is etched from the substrate face to make a concave part, the flexible area is formed in a bottom face part of the concave part, and the round is formed so as to become shaped like R on the boundary between the bottom face part and a flank part of the concave part. The stress applied to the boundary between the bottom face part and the flank part of the concave part when the flexible area is displaced is spread by means of the round, whereby the portion can be prevented from being destroyed.
According to a thirtieth aspect of the present invention, there is provided a semiconductor microvalve comprising a semiconductor device in any of ninth to twenty-ninth aspects and a fluid element being joined to the semiconductor device and having a flow passage with a flowing fluid quantity changing in response to displacement of the moving element. The semiconductor microvalve which has similar advantages in ninth to twenty-ninth aspect of the present invention as well as can be driven with low power consumption can be provided.
In a thirty-first aspect of the present invention, in the thirties of the present invention, the semiconductor device and the fluid element are joined by anodic junction. It is made possible to join the semiconductor device and the fluid element.
In a thirty-second aspect of the present invention, in the thirties aspect of the present invention, the semiconductor device and the fluid element are joined by eutectic junction. It is made possible to join the semiconductor device and the fluid element.
In a thirty-third aspect of the present invention, in the thirtieth aspect of the present invention, the semiconductor device and the fluid element are joined via a spacer layer. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed in the spacer layer and the stress applied to the flexible area can be suppressed.
In a thirty-fourth aspect of the present invention, in the thirty-third aspect of the present invention, the spacer layer is made of polyimide. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed because of elasticity of polyimide and the stress applied to the flexible area can be suppressed.
According to a thirty-fifth aspect of the present invention, there is provided a semiconductor microrelay comprising a semiconductor device as the ninth to twenty ninth aspect of the present invention and a fixed element being joined to the semiconductor device and having fixed contacts being placed at positions corresponding to a moving contact provided on the moving element, the fixed contacts being able to come in contact with the moving contact. The semiconductor microrelay which has similar advantages to those in the invention as claimed in claims 9 to 23 as well as can be driven with low power consumption can be provided.
In a thirty-sixth aspect of the present invention, in the thirty-fifth aspect of the present invention, the fixed contacts are placed away from each other and come in contact with the moving contact, whereby they are brought into conduction via the moving contact. The semiconductor microrelay wherein the fixed contacts placed away from each other can be brought into conduction can be provided.
In a thirty-seventh aspect of the present invention, in the thirty-fifth or thirty-sixth aspect of the present invention, the moving contact and the fixed contacts are gold cobalt. The moving contact and the fixed contacts can be brought into conduction.
In a thirty-eighth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined by anodic junction. It is made possible to join the semiconductor device and the fixed element.
In a thirty-ninth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined by eutectic junction. It is made possible to join the semiconductor device and the fixed element.
In a fortieth aspect of the present invention, in the thirty-fifth to thirty-seventh aspect of the present invention, the semiconductor device and the fixed element are joined via a spacer layer. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed in the spacer layer and the stress applied to the flexible area can be suppressed.
In a forty-first aspect of the present invention, in the fortieth aspect of the present invention, the spacer layer is made of polyimide. The thermal expansion difference between the semiconductor device and the fluid element when they are joined is absorbed because of elasticity of polyimide and the stress applied to the flexible area can be suppressed.
According to a forty-second aspect of the present invention, there is provided a manufacturing method of a semiconductor device in the eighteenth aspect of the present invention prepared by a process comprising the steps of:
etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;
etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;
etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;
filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and
applying a coat of the thermal insulation material to the one face of the semiconductor substrate to form one area forming a part of the flexible area.
The thermal insulation area and one area forming a part of the flexible area are formed of the same material at the same time, whereby the manufacturing process is simplified and the costs can be reduced.
According to a forty-third aspect of the present invention, there is provided a manufacturing method of a semiconductor device in sixteenth aspect of the present invention prepared by a process comprising the steps of:
etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;
etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;
etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;
forming an aluminum thin film as an area defined in the flexible area on the other face of the semiconductor substrate and a wire for applying an electric power to the heating means;
filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area.
whereby the manufacturing process is simplified and the costs can be reduced.
According to a forty-fourth aspect of the present invention, there is provided a manufacturing method of a semiconductor device in seventeenth aspect of the present invention prepared by a process comprising the steps of:
etching and removing one face of the semiconductor substrate to form a bottom face part as one area forming a part of the flexible area;
etching and removing the other face of the semiconductor substrate to form the concave part in the moving element;
etching and removing the other face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;
forming a wire for applying an electric power to the heating means;
filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and
forming a nickel thin film as an area defined in the flexible area on the other face of the semiconductor substrate.
According to a forty-fifth aspect of the present invention there is provided a manufacturing method of a semiconductor device in the first aspect of the present invention prepared by a process comprising the steps of:
etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;
filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and
etching and removing the other face of the semiconductor substrate to form the thermal insulation area.
According to a forty-sixth aspect of the present invention, there is provided a manufacturing method of a semiconductor device in the fifth aspect of the present invention prepared by a process comprising the steps of:
etching and removing one face of the semiconductor substrate to form at least a portion which becomes the thermal insulation area placed between the semiconductor substrate and the flexible area;
forming a reinforce layer in the thermal insulation area;
filling the portion which becomes the thermal insulation area with a thermal insulation material to form the thermal insulation area; and
etching and removing the other face of the semiconductor substrate to form the thermal insulation area.
This invention is carried out paying attention to the fact that a resin material such as polyimide or a fluoridated resin has high heat insulation properties (about 80 times those of silicon dioxide) and further is liquid and easy to work and that a thin film having any desired thickness (several xcexcm to several ten xcexcM) can be easily provided by a semiconductor manufacturing process of spin coat, etc.